Why conspiracy theories exist that FDR knew in advance of the coming attack on Pearl Harbor

I was once on a bike ride across the Alps with a few American cyclists, and one member of the group told the group at dinner about a book that claimed that President Franklin Roosevelt knew about the coming attack on Pearl Harbor, but hid it from the public, because FDR wanted to get the country into war with Japan. I dismissed that idea with annoyance, but now I see where the idea came from, by reading part of the book “1941” by Marc Wortman.

It is true that FDR expected war with both Japan and Germany. FDR was atually hoping that the Germans would attack U.S. shipping in the Atlantic, thus giving him an excuse to declare war. This was not because he liked war, but because Britain sorely needed help at that time and ships bringing American supplies were being sunk by U-Boats in the Atlantic. As far as Japan went, however, the U.S. wanted to avoid giving the Japanese any excuse to attack, though informed Americans realized that war was coming. The more time the U.S. had to avoid a confrontation, the more ships and planes it could build. It is interesting that journalist William Shirer, in a talk to an audience in Milwaukee, predicted a showdown with Japan within four weeks. He made this prediction on November 10. The attack came on December 7.

On November 25, Roosevelt met with his War Council and told the men that an attack was likely, perhaps to come as early as the following Monday. Wortman writes that FDR:

thought the Japanese would carry out their initial move without declaring war, [and]…raised the possibility of “maneuver[ing] them into the position of firing the first shot without allowing too much danger to ourselves.”

Those remarks are the incriminating quote that raised the specter of FDR wanting an attack on Pearl Harbor, without having protected it adequately first.

The truth, however, is that the Americans thought the attack from Japan would either be on Russia, which at that time was being invaded by Germany and had its hands full, or would be on Southeast Asia.

Americans thought of Oahu as a strong fortress that would deter any attack. This turned out to be a huge mistake. On November 26, the most powerful air and sea force ever assembled, the “Kido Butai” sailded out of the Kurile islands. This Japanese force consisted of six carriers carrying 414 fighters and bombers, accompanied by two battleships, three cruisers, nine destroyers, eight tankers, 23 submarines and eight min-submarines. Its destination was Pearl Harbor.

I remember one story from that period – an American officer on a ship deck, crying as he shot an ordinary gun at the Japanese planes in the sky.